This invention relates to clipper blades (toothed blades) of a power working machine, and in particular to the clipper blades of a hand-held power working machine such as a hedge trimmer.
A hand-held power working machine such as a hedge trimmer is generally constituted by a prime mover case having a prime mover such as an internal combustion engine, a mount base portion surrounding a transmission case having a power transmission device such as gears to be actuated by the prime mover, a working portion comprising the clipper blades to be actuated via the aforementioned power transmission device by the prime mover, and a handling portion attached to the prime mover case or the mount base portion. This handling portion is constituted, for the convenience of manipulation thereof, by a front handle portion and a rear handle portion.
As shown in FIG. 3, the blade portion of the conventional working portion is constituted by a pair of upper and lower clipper blades 40 and 50, each of which having not only a plurality of triangular cutting edges 41 and 51 respectively, but also a plurality of guiding slots 42 and 52 respectively which are formed along the whole length of the clipper blades 40 and 50 at predetermined intervals.
An upper blade-supporting plate 60 is disposed on the upper surface of the upper clipper blade 40, and a lower blade-supporting plate 70 is disposed at the bottom surface of the proximal end portion of the lower clipper blade 50. The upper blade-supporting plate 60 is provided with a plurality of threaded holes 62.
The pair of the upper and lower clipper blades 40 and 50 are supported or cantilevered by means of the upper blade-supporting plate 60. Specifically, a plurality of guiding male screws 61 are introduced from the bottom side of the lower clipper blades 50 into the guiding slots 52 and 42, and further screwed into the threaded holes 62. The upper portions 61a of the guiding male screws 61 that have been protruded from the threaded holes 62 are screwed and clamped with locknuts 71. As a result, the pair of the upper and lower clipper blades 40 and 50 are respectively guided by the combination of the guiding male screws 61 with the guiding slots 42 and 52 so as to permit them to slide reciprocatingly in the longitudinal direction thereof.
The upper and lower clipper blades 40 and 50 are actuated, via an eccentric cam, etc. disposed in the transmission case, by the internal combustion engine so as to be reciprocatingly moved in opposite direction to each other with a phase shift of 180 degree, thus making it possible to carry out the cutting work of vegetation.
Because of the specific structure that the pair of the upper and lower clipper blades 40 and 50 are extended from and cantilevered by the main body of a hand-held power working machine such as a hedge trimmer, as well as because of the weight of the upper and lower clipper blades 40 and 50 which are made from a steel plate having a thickness of 2.5 mm (even though they are somewhat lightened by the formations of guiding slots 42 and 52), the cutting work with this hand-held power working machine by carrying the machine with both hands is very hard for an operator due to this cantilever type clipper blades 40 and 50.
Further, since the guiding slots 42 and 52 are formed only at the portions of the upper and lower clipper blades 40 and 50 where the several guiding male screws 61 are to be introduced for guiding these slots 42 and 52, the quenching rate at the occasion of heat treatment in the manufacture of the clipper blades 40 and 50 becomes non-uniform depending on the portion of the clipper blades 40 and 50, thus giving rise to the generation of strain or crack in the clipper blades 40 and 50. Furthermore, a stress concentration tends to occur at these slot portions during the operation of the clipper blades 40 and 50, thus giving rise to the generation of crack at these slot portions.